1. Field of the Invention
This invention relates to a method and apparatus for drilling optimum boreholes in the earth, to methods for calculating such optimum boreholes, and to methods and apparatus for drilling such boreholes having minimum tortuosity.
2. Description of the Prior Art
Drilling non-vertical boreholes in the earth to reach one or more points under the surface of the earth containing petroleum is common practice today. However, even with modem techniques and apparatus, the borehole is not an optimum trajectory to the particular subsurface point.
The actual trajectory may differ greatly from the planned trajectory. The path may be long and tortuous so that the length of the hole and the drill string friction are greatly increased.
The human controlling the drilling apparatus may use measurement-while-drilling apparatus ("MWD") to determine the drill bit location. The human may then use a simple nomograph to project the drilling parameters. Last, the human makes adjustments to the drilling apparatus using experience to correct for uncalculated and unmeasured but important parameters.
Basically, the process is somewhat analogous to a human trying to point a rifle to hit a known target but not knowing the direction of the wind or exactly the path the bullet will take. The rifleman could do much better if the rifleman knew the location and heading of the bullet at each measurement and could change the bullet's direction. Then the rifleman could direct the bullet along the optimum path to the target.
To drill a borehole meeting a specific criterion requires adjustments immediately after receiving the measurement-while-drilling data. A human cannot make the necessary calculations quickly enough to determine the correct drilling apparatus instructions considering the huge amount of data and the difficulty of the calculations.
Last, some characteristics of the trajectory are so important, that those characteristics form the criteria to judge the optimum path. One such characteristic is the tortuosity of the path. One large petroleum company has suggested paying the drilling contractor based on minimizing tortuosity. This is further discussed in Increasing Extended-reach Capabilities Through Wellbore Profile Optimization, Banks, S. M., Hogg, T. W., Thorogood, J. L., Drilling Conference--Proceedings Drill Conference Proceedings, Society of Petroleum Engineers of AIME, Richardson, Tex., USA. p 85-90, 1992.
Prior methods have included hand calculations, nomograph and computer programs to calculate the planned drilling paths. Literature in which others have discussed methods of general calculation principles are as follows:
An Improved Method for Computing Directional Surveys, Wilson, G. J., Journal of Petroleum Technology, 871-876, August 1968; PA1 Computerized Well Planning for Directional Wells, Hodgson, H., Varnado, S. G., Paper SPE 12071, 58th Annual Technical Conference, Society of Petroleum Engineers, Published by Society of Petroleum Engineers of AIME, Richardson, Tex., USA, 1983; PA1 Evaluating and Planning Directional Wells Utilizing Post Analysis Techniques and a Three Dimensional Bottom Hole Assembly Program, Paper SPE 8339, 54th Annual Technical Conference, Society of Petroleum Engineers, Published by Society of Petroleum Engineers of AIME, Richardson, Tex., USA, 1979; and Applied Drilling Engineering, Bourgoyne, A. T., Jr., Millheim, K. K., Chenevert, M. E., Young, F. S., Jr., Society of Petroleum Engineers, Richardson, Tex., 353-359,366-372, 1986. PA1 Directional Well Planning with Multiple Targets in Three Dimensions, Goldman, W. A., Paper SPE 18791, California Regional Meetings, Society of Petroleum Engineers, Published by Society of Petroleum Engineers of AIME, Richardson, Tex., USA, 1989; and PA1 Artificial Intelligence Enhances Directional Control, Goldman, W. A., 65 Petroleum Engineer International 15-22, February 1993, the text of each such reference being incorporated herein by reference for all purposes.
The applicant herein has published methods of directional well planning in three dimensions in:
The applicant in Artificial Intelligence Enhances Directional Control, Goldman, W. A., 65 Petroleum Engineer International 15-22, February 1993 presented the algorithm for a survey driven trajectory planning system and discussed the capability of an automated system. That article also discusses the three dimensional bit walk calculations.
Other prior art literature in the area are the following articles: Increasing Extended-Reach Capabilities Through Wellbore Profile Optimization, Banks, S. M., Hogg, T. W., Thorogood, J. L., Drilling Conference--Proceedings Drill Conference Proceedings, Published by Society of Petroleum Engineers of AIME, Richardson, Tex., USA, p 85-90, 1992; and Relief Well Technology Can Solve Ordinary Problems, Wright, J., Oil and Gas Journal, 30-33, Jan. 18, 1993. Magnetic Ranging Tool Accurately Guides Replacement Well, Lane, J. B., Wesson, J. P., Oil and Gas Journal, 96-99, 21 Dec. 21, 1993.
Applicant is not aware of any references which discuss automated control using measurement-while-drilling telemetry data while drilling nor the direct control of the drilling apparatus based on the measurement-while-drilling telemetry data, much less following an optimum path, except applicant in Artificial Intelligence Enhances Directional Control, Goldman, W. A., 65 Petroleum Engineer International 15-22, February 1993. Further, a method to minimize borehole tortuosity has not heretofore been known in the drilling industry.
A new and more efficient method of drilling boreholes from the surface to a subsurface point along the optimum trajectory is needed. Solutions to the optimization three dimensional drilling problem considering bit walk and other unknown subsurface anomalies are needed but before this invention were unavailable. Further, the importance of minimizing tortuosity needs to be a key part of the optimization process. This invention addresses such prior needs.